1. Field of the Invention
The present invention relates to an ultrasonic diagnosis apparatus adaptable to contrast echo imaging diagnosis, and a control method thereof.
2. Description of the Related Art
An ultrasonic imaging diagnosis apparatus displays a tomographic image of tissue through a non-invasive examination method using an ultrasonic wave. The ultrasonic imaging diagnosis apparatus is quite useful at clinics, for example, beat pulsation of the heart or motion of a fetus can be displayed in real time through a manipulation as simple as placing an ultrasonic probe to the body surface, a screening can be performed repetitively owing to its high safety, and it can be moved to a bedside for a screening to be conducted owing to its small system size in comparison with other diagnosis equipment for X-ray imaging, CT imaging, MRI, etc. In addition, although an ultrasonic diagnosis apparatus differs extensively depending on the types, there has been recently developed an ultrasonic diagnosis apparatus so small in size that one can carry it around with one hand. There is a possibility that an ultrasonic diagnosis apparatus the patient can manipulate by himself will be developed in the near future.
Incidentally, with the recent commercialization of ultrasonic contrast media of an intravenous infusion type, an ultrasonic diagnosis through the contrast echo imaging method has been becoming popular. The contrast echo imaging method is aimed at evaluating the dynamics of a blood flow, for example, in a screening of the heart, the abdominal organs and the like, by introducing an ultrasonic contrast medium into a vein and thereby enhancing a blood flow signal. Many of contrast media use micro-bubbles as sources of reflections, and the higher the quantity and concentration of the introduced contrast medium become, the higher the effect of contrast imaging becomes. On the other hand, it has been known that bubbles, being a delicate base material by nature, collapse upon irradiation of ultrasonic waves, which shortens an effective time for contrast imaging.
In general, a blood flow often means red blood cells. Ideally speaking, it is preferable that a contrast medium used for an ultrasonic diagnosis shows the same dynamics as those of the red blood cells. In practice, however, the contrast medium is now known to have dynamics different from those of the red blood cells.
For example, many of ultrasonic contrast media are known to cause retention in the parenchyma of the liver, and it is thought that foreign-body uptake cells in the sinusoid of the liver ingest the retained contrast medium (needless to say, the red blood cells are not ingested). Also, blood capillaries within the body include cavities of a size that allows a liquid component (blood plasma) to seep out, so that cells are supplied with nutrition or oxygen. Although the cavities of the blood capillaries are too small of a size for the red blood cells to pass through, it is predicted that some of contrast media leak to the outside through the cavities in the blood capillary wall depending on the bubble size (the average diameter of the red blood cells is approximately 8 μm, and it is thought that the bubbles of a contrast medium having a size of approximately 8 μm at the maximum and 0.5 μm or less at the minimum are circulating throughout the body).
However, it remains unclear whether the contrast medium constantly reflects the dynamics of circulating blood, and for example, in a case where bubbles are retained in a micro circulation system, ecological information using the destruction of bubbles as the sources of echoes may not reflect the dynamics of circulating blood. In such a case, it may become difficult to observe the true dynamics of the red blood cells even when enhancement in intensity by a contrast medium is achieved.
The invention was devised in view of the foregoing situations, and therefore provides an ultrasonic diagnosis apparatus capable of observing or quantifying bubbles of a contrast medium of a size comparable to the red blood cells and bubbles of the contrast medium of a sufficiently smaller size independently through control of a degree of disappearance of the bubbles by changing transmission conditions.